Unlike rifles used for hunting wild game for sport, standard firearms used by military services are typically designed for use against human targets, at long range, and with precise accuracy. The ammunition best suited for the foregoing requirements is usually not large in caliber of the projectile, but having a shell casing adapted to holding a large quantity of powder. Such ammunition, as used for most military firearms, is of the center fire type requiring a small ignition cap mounted at the center in the base of each round to ignite the main powder charge.
The manufacturing cost of ammunition such as that described above is understandably high, and involves larger quantities of metal and powder than would small rounds such as the familiar .22 caliber rounds widely used for hunting small game and for inexpensive target-practice by the general public. The latter type of ammunition characteristacally has a volume of powder not much larger than the volume of the projectile itself, and has no cap in the shell base since it is rim fired. For training purposes, where simple handling and target practice with military firearms is taught to recruits, it would obviously be a very substantial saving in dollars as well as conservation of materials if such firearms could be adapted to use very small caliber ammunition in place of the lethal type for which the weapons were originally designed. Moreover, smaller and more accessible firing ranges are adequate for training when the smaller ammunition is used.
A Rifle Conversion Assembly U.S. Pat. No. 3,771,415 issuing to Henry A. Into et al Nov. 13, 1973, and a Weapon Conversion Bolt Assembly Device U.S. Pat. No. 3,776,095 issuing to Maxwell G. Atchisson, Dec. 4, 1973, relate to devices for converting a firearm of one caliber to one of a smaller caliber. They provide for a unitary bolt assembly that may be substituted for the standard bolt assembly in the weapon. They include a conversion chamber adapter with a bolt mounted for movement between recoil and battery positions. They each have a backplate damper to assist in maintaining the operating components in assembly and to absorb recoil impact energy of the bolt upon firing of the weapon. The bolt slides longitudinally between the conversion chamber and the backplate damper. An extractor and firing pin ride on the bolt and an ejector is positioned on the assembly frame to eject cartridge casings as the bolt recoils rearwardly when a cartridge has been fired.
The foregoing conversion assemblies, however, do not satisfy two safety requirements in that they may cause double firing and the rear of the rifle chamber cannot be visually inspected at the end of firing since their bolts cannot be held out of battery position.